Mix Mastering - Skills of Paul Bryant and how he works on the stereo master, balances treble and bass, volume of the tracks and makes the CD sound "more expensive". Use of specific mastering person who is an expert in the area.
Chris Shepard at Chicago Recording Company doesn't need to "fix" things, because he does it right the first time. We can all use a little enhancement, though -- and Chris is not above it either. Hear how he uses his Pultec EQP-1A3 to aid in this process.